Bridges with unequally spaced girders

In bridge design, unequal girder spacing is required in special instances such as in staged construction during bridge replacement and in widening of an existing bridge. The simple formulas for estimating live-load distribution factors contained in the 1992 AASHTO code are intended for use with bridges with uniform girder spacing and generally result in conservative bridge designs, especially for bridges supported by W-shape girders. In contrast, the new bridge design code would take advantage of refined analysis methods for predicting distribution factors. These factors were recently shown to have particular advantages for bridges with unequally spaced girders. In this study, a finite element-based refined method was employed in an attempt to derive more accurate live-load distribution factors. Comparisons of maximum flexural distribution factors for interior I-shaped girders determined from various methods are shown.